It has become conventional in the construction of motion chairs which are also platform rockers, to provide some type of locking mechanism that is active between the part of the chair that rocks and either the part of the chair that remains stationary or the floor. Typically, such locking mechanisms are in a non-active state, either disengaged or free to move, so long as the movable part of the chair remains upright, but to become activated as soon as the movable part has tilted, has reclined or the ottoman is raised to such a degree that the user can be expected to have his or her feet off the floor and no longer able to control rocking by a combination of foot pressure on the floor and forward rear pivoting motion of the upper body, i.e. just as a loss of control event is about to occur.
Several different types of locks have been developed. In one type, one or more crankable links are each provided at the free end with a roller or equivalent skid. This link is operatively connected to some part of the chair frame or motion chair mechanism which makes a characteristic relative movement at the time that the aforementioned loss of control event is about to occur in such a manner as to cause the free end of the lock link to engage the chair base or the floor and become a strut active in compression and/or in tension for bracing the rockable part of the chair against rocking. Thereafter, as the chair is brought back to an erect condition, and/or the ottoman is lowered to the point where the user can again exert control by pushing his or her feet on the floor, the aforementioned characteristic relative motion, occurring in reverse, or in an equivalent manner is used for withdrawing the free end of the link away from the chair base or floor, so that rocking is again possible. Perhaps due to some physical similarity of these locks, their function and/or manner of deployment and retraction, locks of this type often have become nicknamed "landing gear", after the like-named structures of aircraft.
Typically in a motion chair having a landing gear-type rocker lock when mounted forwardly of where the rocker cams run on the side rails of the base, mere engagement of the free end of the lock link with a touch-down pad on the base, or with the floor under or to the front of the chair will prevent forward rocking, but will not prevent rearward rocking. On some chairs this is sufficient, because the chair/occupant composite center of gravity shifts in such a way during its tilting, reclining and/or ottoman-elevating motion that the composite of the center of gravity of the use and rockable part of the chair is located forwardly of the rocker cam/rail engagement and rear rocking need not be protected against because it is so unlikely to occur. In other instances, use of a forwardly-located merely-engaged landing gear-type rocker lock is acceptable because some other type of rocker lock, e.g. one of the ratchet and releasable pawl-type is also provided and coordinately activated to prevent rearward rocking.
In cases where a forwardly-located landing gear-type rocker lock is provided and must serve to prevent both forward and rear locking, a trap is conventionally provided for the free end of the strut. As the chair is tilted, reclined and/or its ottoman is raised, the free end of the landing gear strut is pivoted into the trap, which is a claw-like or cage-like element mounted on the chair base. This element is shaped to secure the free end of the landing gear strut so that not only does the strut perform as a brace in compression to prevent forward locking, but it also performs as a tensile tie to prevent rearward rocking.
On other motion chairs, the landing gear-type rocker blocking mechanism provides its strut to the rear of where the rocker cams ride on the side rails, so that mere engagement with a touchdown pad is sufficient to prevent rearward rocking, but a cage, or some auxiliary rocker lock is required for preventing forward rocking.
In addition to landing-gear types of rocker locks, the prior art includes ones of the aforementioned ratchet and releasable pawl type, ones of the toggled links type, ones where a tubular slider mounted to the rockable part of the chair is constructed and arranged to releasably grip a fixed bar, and possibly other diverse types of locks.
Many conventional rocker locks are provided in duplicate as more or less integral parts of the left and right side linkages further complicating the design and installation of these already often baffling complex members and adding to the difficulty of manufacturing and mounting them. Further, such rocker locks often are fairly organic to the side linkages for which they were designed, so that design costs cannot be spread over a plurality of different side linkage designs so the benefit of long production runs sometimes cannot be achieved. Demand for the rocker locks depends on the demand for the particular design of side linkages of which they form a part.
Some advantages are to be gained from separating the rocker lock from the side linkages, e.g. so that the same rocker lock can be used on chairs having different designs of side linkages, and for achieving a locked condition which imparts a secure, stable feeling to the chair user in spite of the effects of mass production and wear on motion chair hardware geometry and fit.
Some conventional rocker locks which are separate from side linkages are installed intermediate the side linkages, e.g. near the longitudinal centerline of the chair. When such a rocker lock is laterally offset somewhat from the longitudinal centerline of the chair, often it is because a compromise was required between the desire to center the rocker lock and the need to prevent a user who is heavy or sits down hard on the chair from bottoming-out the springing means of the chair seat, on a part of the rocker lock. Stated another way, there has been a heretofore unfilled desire in the art to provide rocker lock that is independent of the motion chair side linkages, which, when activated, locks the chair against both forward and rear rocking, and which can be medially located on the chair without interfering with user comfort.